The geological issues of the Fukushima Daiichi

Given their "floating box", bottom-heavy construction, I cannot see any significant risk of them collapsing, cracking, or even tilting just because that rock is "not strong enough". ...
However, the floating box construction seems to give some protection against that possibility.

The problem is we don't know if it's a real floating box design. I have tried to find out information about Fukushima I foundation type but hasn't been able to find it. Anybody else luckier?
Just because there is a thick bottom concrete doesn't make it a floating box. If it's a floating box design then all of the bottom concrete is a supporting structure. To build it like this is expensive.
If it's not a floating box then there are weaker parts and stronger parts in the bottom concrete.
Another interesting thing is do they have http://en.wikipedia.org/wiki/Base_isolation" [Broken].
I guess the simplest/cheapest design would be this: there are footings that support the weight of the building and then there are beams to transfer weight from one footing to another if there happened to be a landslide underneath one footing.
These are interesting things to study on their own.

Also, such fault-like cracks presumably start deep underground, so they should occur with the same relative displacement and same probability, no matter what the rock type.

I think we have to separate two things here.
The first thing is a crack which is directly created by a fault line. I have an impression that these cracks rarely cut through hard rocks in Fukushima area although now this has happened:

Some of these faults CUT through these hard rocks, which people, including many geologists, thought quite unusual (if not impossible) utill they saw the consequence of the 3-11 Earthquake in Tohoku.

The second thing is the shaking of the ground itself. When the ground is shaking the weaker soil on top of the hard rock could (or could not) amplify the shaking.
How much this has happened in the Fukushima area is again an interesting thing itself.

However, the underground water flow at Fukushima Daiichi seems to be slow and directed towards the ocean. So any leakage through that route should not spread inland, and should be small compared to the oceanic contamination that has already occurred.

I agree. And the radioactive levels of seawater have been decreasing so we know there should be no big leaks from polluted groundwater into the sea. This would suggest that deeper groundwater is perhaps not that polluted at all.

However there is no need to speculate about this point, since TEPCo very early on published the maximum ground acceleration registered in each building during the 3/11 earthquake (and, IIRC, some of those numbers were well above the values assumed in the plant's design).

As far as I see it, there are larger issues concerned.

At one point there was a news report where TEPCO said it cannot deny the possibility that in the number #3 reactor some major damage could have been done by the earthquake itself (I think it was a piping system).

It will take many years until they will finally conclude did the earthquake itself cause any major problem. And who is going to study it? TEPCO itself or some independent research team? (I hope the latter and I hope also not just an IAEA team.)

If at the end they would conclude that the earthquake itself actually did cause some major damage they would also start to find reasons behind it.

One thing is of course that ground acceleration numbers were above design parameters. But at this point they could also question if the whole plant has been built in a proper place / in a proper manner (soil amplification & foundation type etc).

The soil amplification studying as a branch of science is quite young, AFAIK, at least when it concerns the actual maps over different areas. Perhaps the theories are older. For instance: do they have soil amplification maps all over Japan? When I studied a little bit soil amplification maps from the U.S. I noticed some of them were made only quite recently. Like this one was presented in 2002, perhaps made a couple of years earlier:http://gsa.confex.com/gsa/2002NC/finalprogram/abstract_31500.htm

So even if we don't know how is it going to proceed it is still an interesting thing to study. How well are the soil amplification aspects understood all over the world? What kind of foundation types are they using when they are not building on a top of granite/other hard rock? Should a proper soil amplification study be required in the future when building in seismic areas? How about existing NPP:s, should we force them to make soil amplification studies if none exists for that area?

These are interesting questions and I think one can study it a little further without speculating. Like: What kind of foundation type do they really have in Fukushima? Do they have soil amplification maps all over Japan?

Wave velocity by itself is a very unreliable indicator of competency.
You really do need to also study the structural geology when considering sensitive structures.

Earlier I proposed that S-wave velocity could be used as some kind of indicator how strong the rock is. Well, this perhaps applies to some extent but to make a precise analysis more information is needed.

I came across the following in an article in the German daily "Die Welt" published on March 15 about whether or not contamination of the water table was likely, which talks about the local type of rock:

English translation by me:

As shown by geological maps and data from drilling, the ground consists of claystone, a fine grained rock from clay minerals and quartz. The slate-like rock originates from clay-like ocean sediments beyond the coast, which was solidified over millions of years by high pressure in the crust of the earth. Claystone is known to be relatively water impermeable.

"The material is apparently homogeneous and originates from the Pliocene two to five million years ago," says Andreas Küppers of the Deutsches Geoforschungszentrum (GFZ, German Geo Research Centre) in Potsdam. "The probability is high, that this type of rock is impermeable and will not permit contact to aquifers", says the geologist, who personally had been working in Japan for several years and also got to know the power plant in Fukushima at the time. The clay layer measures at least 200 m in depth - as evidenced by geological engineering profiles produced ahead of construction of the plant based on drilling. Possibly the clay rock is even much deeper, but the drilling didn't cover that.

The article mentions that around the power plant several metres of sandstone sit on top of the claystone, but it was removed where the foundations were built, for example at unit 3 where these foundations reach 16 metres deep.

It also mentions that the base of the foundations is a 4 metre thick slab of reinforced concrete.

You can use Google translate or Google Chrome to read a rough translation of the complete article into the language of your choice.

My question for tonio: In one paper TEPCO said they are going to empty the contaminated sub-drain pits of the unit #1 - #4 at some point. How is it controlled that these sub-drain pits won't overflow? Is there some kind of automatic measurement of the water level in the sub-drain pits or are they controlled manually?

I have not noticed TEPCO saying that they have emptied the unit #1 - #4 pits. For units #5 - #6 they did it a long time ago. There might be more groundwater near #5 - #6 than #1 - #4.

What is the best university to study geology in Australia? I have applied for a BAs(geology) at UWA and don't know whether I have chosen the right uni. Are there any better ones to go to? Also, what are the chances of getting a job after completing the BAs in geology in the resource sector for Australia, I thought it looks good so thats why I'm changing my career. I'm 27 now and thought I still have time :) let me know your thoughts. Thanks!